Is the D driver external or just another partition of the internal drive? If it is not external and simply another partition with truely nothing on it, they I would use a partition expanding program to get rid of the D partition and increase the size of the C partition. As somebody mentioned earlier some programs don't play nice if they are not installed on the same partition/volume as Windows. In my experience over the years extra drives and partitions are great for data but a disaster for installing programs.

toddz